This invention relates to the recovery of nitrated esters from water. In another aspect this invention relates to purification of the wash or process water of explosive manufacturing processes where it is desirable to recover substantially all of the nitrated esters contained in the water prior to its release. Still another aspect of this invention relates to the separation of an aqueous solution which contains minor amounts of nitrated esters of polyalcohols which are only slightly soluble in water. Further, this invention relates to the extraction of dissolved portions of nitroglycerin from an aqueous solution by contacting said solution with ethylene glycol dinitrate.
The commercial production of glycerol nitrate (also known as nitroglycerin) and ethylene glycol dinitrate, for example, for explosive compositions normally involves operations including nitration, separation of spent nitric acids and purification by neutralization and washing. During the purification and washing steps, large volumes of water are used which come into contact with the nitrated esters. Because the solubility of these nitrated esters in water is very low, the water and a major portion of the nitrated esters can be separated easily. However, a limited quantity of the nitrated esters is dissolved in the wash or process water and heretofore has been discharged with the water phase. Presently, the water effluents only contain the amounts of nitrated esters which can be dissolved in the water. That is, for reasons of safety, the effluent water contains amounts of nitrated esters which do not exceed the saturation point of the water at the temperature at which it is discharged. Recently, however, the Environmental Protection Agency has proposed more stringent effluent limitations and guidelines regarding the maximum COD (chemical oxygen demand) and BOD (biological oxygen demand) which effluents from explosive manufacturing plants may have. See E.P.A. Proposed Regulation, Section 457.10-457.12, 41 Fed. Reg. 10184 (1976). Because COD requirements are directly related to the concentration of the nitrated esters in the effluent water, a process for the removal of nitrated esters which have become dissolved in the water is desirable.
Recently, it has been discovered that aqueous solutions containing dissolved nitrated esters of polyalcohols such as nitroglycerin, ethylene glycol dinitrate, 1,2-propylene glycol dinitrate, and 1,3-propylene glycol dinitrate, for example, which are all characterized as being only slightly soluble in water, can be separated by distilling the aqueous solution at temperatures in the range of from about 50 degrees to about 200 degrees F. under pressures of from about 10 to about 500 mm of mercury. This process is set forth in detail in applicant's co-pending application entitled "RECOVERY OF NITRATED COMPOUNDS FROM WATER", Ser. No. 721,773, filed Sept. 9, 1976, now U.S. Pat. No. 4,066,514, which is hereby incorporated by reference. This process provides a very effective means for separating a major portion of the dissolved nitrated esters found in waste water of explosive manufacturing plants. While both nitroglycerine and ethylene glycol dinitrate, for example, can be separated from waste waters in this manner the above described process is much more effective in the separation of ethylene glycol dinitrate than for nitroglycerine. Therefore, a process whereby the nitroglycerine contents of wash and process waters of explosive plants can be reduced below the levels obtainable with the above-described distillation process is desirable.